Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $57.60   9.395%   $63.0115   $63.01   $63.00   $63.00  
  Purchase #2 $164.77   8.696%   $179.0984   $179.10   $179.10   $179.10  
  Purchase #3 $23.74   9.587%   $26.016   $26.02   $26.00   $26.00  
  Purchase #4 $15.97   4.371%   $16.668   $16.67   $16.65   $16.70  
  Purchase #5 $118.41   9.818%   $130.0355   $130.04   $130.05   $130.00  
  Purchase #6 $49.62   10.419%   $54.7899   $54.79   $54.80   $54.80  
  Purchase #7 $199.93   13.685%   $227.2904   $227.29   $227.30   $227.30  
  7 purchase totals = $630.04       $696.9097   $696.92   $696.90   $696.90